Nanocrystalline Ag₃PO₄ for Sunlight- and Ambient Air-Driven Oxidation of Amines: High Photocatalytic Efficiency and a Facile Catalyst Regeneration Strategy

Abstract

Selective oxidation of amines to imines using sunlight as clean and renewable energy source is an important but challenging chemical transformation because of high reactivity of the generated imines and lack of visible light-responsive materials with high conversion rates. In addition, oxygen gas has to be purged in the reaction mixture in order to increase the reaction efficiency which, in itself, is an energy-consuming process. Herein, we report, for the first time, the use of Ag 3 PO 4 as an excellent photocatalyst for the oxidative coupling of benzyl amines induced by ambient air in the absence of any external source of molecular oxygen at room temperature. The conversion efficiency for the selective oxidation of benzyl amine was found to be greater than 95% with a selectivity of >99% after 40 min of light irradiation indicating an exceptionally high conversion efficiency with a rate constant of 0.002 min −1 , a turnover frequency of 57 h −1 , and a quantum yield of 19%, considering all of the absorbed photons. Ag 3 PO 4 , however, is known for its poor photostability owing to a positive conduction band position and a favorable reduction potential to metallic silver. Therefore, we further employed a simple catalyst regeneration strategy and showed that the catalyst can be recycled with negligible loss of activity and selectivity.

In Site Generation of Well‐Dispersed Ag3PO4 NPs on Protein‐Inorganic Hybrid Nanoflowers with Enhanced Catalytic Performance

“…[12] After modification, new diffraction peaks at 2θ = 33.29°, 36.5°, 52.61°, 57.2°, and 61.6°were in accordance with the cubic structure of Ag 3 PO 4 (JCPDs card number 06-0505). [13] In addition, as shown in Figure 3B, FT-IR spectra have also provided direct proof for the chemical structures of BSAinorganic hybrid nanoparticles. The peak at 1145 cm À 1 of Cu 3 (PO 4 ) 2 @BSA was attributed to the bending vibration of CuÀ OH (ν3 bending mode).…”

“…As shown in Figure 3A, the positions and intensities of the diffraction peaks confirmed the excellent crystallinity of the products, which are consistent with Cu 3 (PO 4 ) 2 ⋅ 3H 2 O (JCPDs card number 22‐0548) . [12] After modification, new diffraction peaks at 2θ=33.29°, 36.5°, 52.61°, 57.2°, and 61.6° were in accordance with the cubic structure of Ag 3 PO 4 (JCPDs card number 06–0505) [13] …”

Chromophore‐Inspired Design of Pyridinium‐Based Metal–Organic Polymers for Dual Photoredox Catalysis

“…The cross‐coupling reaction was completely inhibited by addition of excess 2,2,6,6‐tetramethylpiperidinooxy (TEMPO) or 2,6‐di‐tert‐butyl‐4‐methylphenol (BHT), suggesting the reaction undergoes a radical pathway (entries 1 and 2) [24] . KI and AgNO 3 , respectively as hole and electron scavengers, also induced an entire loss of reaction efficiency, implying that both holes and electrons played important roles in this photoredox system (entries 3 and 4) [25] …”

“…[24] KI and AgNO 3 , respectively as hole and electron scavengers, also induced an entire loss of reaction efficiency, implying that both holes and electrons played important roles in this photoredox system (entries 3 and 4). [25] Based on the above results and the model electrontransfer system shown in Scheme 1, we proposed a reaction mechanism for α-amino C(sp 3 )À H arylation and monofluoroalkenylation of amines (Scheme 2). Under irradiation by visible light, the photoexcited [PYTC + ]* is easily engaged in a SET process with N-phenylpyrrolidine to release groundstate [PYTC] * and radical I. Deprotonation of I delivers αamino radical II.…”

A Keggin-type polyoxometalate-based metal–organic complex as a highly efficient heterogeneous catalyst for the selective oxidation of alkylbenzenes

“…Recently, polyoxometalates (POMs) as a kind of functional material have attracted wide attention because of their potential applications in the field of catalysis, [15][16][17] batteries, 18,19 supercapacitors, 20,21 and electrochemistry. 22,23 Particularly, some POMs can be used as catalysts for efficiently catalyzing the oxidation of various alkylbenzenes; [24][25][26][27][28] however, they have the disadvantages of limited reaction modes and high solubility, which limit their application. 29,30 To solve this problem, some POMs have been introduced into complexes to form insoluble POM-based metal-organic complexes (POMOCs), which are attractive in the following three aspects.…”